The present invention relates to the hydrodynamics of marine vessels, more particularly to adjuncts, appendages and auxiliary devices for affecting same.
A stem flap is an extension of the hull bottom surface which extends aft of the transom. It is a relatively small appendage (typically constructed so as to include internal metal bracing beams and external metal plate material) which is fitted to the ship""s transom. Critical stern flap geometry parameters include: (i) chord length, (ii) span across the transom; and, (ii) an angle denoted as xe2x80x9ctrailing edge downxe2x80x9d (TED), referenced to the local buttock slope (run) at the transom. The main purpose of a stern flap device is to reduce the shaft power required to propel a ship through the water, thereby reducing the engine""s fuel consumption and increasing the ship""s top speed and range.
The application of stern flaps to large displacement vessels is a fairly recent innovation. The U.S. Navy has been investigating the use of stern flaps on many different hull types. Stern flaps have now been proven by the U.S. Navy to reduce the requisite amount of propulsive power during navigation, with several concomitant advantages. Stern flaps: foster reductions in operating and life-cycle costs through fuel savings; increase both ship speed and range; decrease the amount of pollutants released by ships into the atmosphere; and, reduce propeller loading, cavitation, vibration and noise tendencies.
Incorporated herein by reference is the following United States patent which is pertinent to stern flaps: Karafiath et al. U.S. Pat. No. 6,038,995 issued 21 Mar. 2000, entitled xe2x80x9cCombined Wedge-Flap for Improved Ship Powering.xe2x80x9d The following papers, each of which is incorporated herein by reference, are also pertinent to stern flaps: Karafiath, G., D. S. Cusanelli, and C. W. Lin, xe2x80x9cStem Wedges and Stern Flaps for Improved Poweringxe2x80x94U.S. Navy Experience,xe2x80x9d 1999 SNAME Annual Meeting (paper), Baltimore, Md. (September 1999); Cusanelli, D. S., xe2x80x9cStern Flapsxe2x80x94A Chronicle of Success at Sea (1989-2002),xe2x80x9d SNAME Innovations in Marine Transportation, Pacific Grove, Calif. (May 2002); Cave, W. L., and D. S. Cusanelli, xe2x80x9cEffect of Stem Flaps on Powering Performance of the FFG-7 Class,xe2x80x9d SNAME Chesapeake Sect Paper, (October 1989); Cusanelli, D. S., and W. L. Cave, xe2x80x9cEffect of Stern Flaps on Powering Performance of the FFG-7 Class,xe2x80x9d Marine Technology, Vol. 30, No. 1, pp 39-50, (January 1993); Cusanelli, D. S., and K. M. Forgach, xe2x80x9cStem Flaps for Enhanced Powering Performance,xe2x80x9d Proceedings of 24th ATTC, College Station, Tex. (November 1995); Cusanelli, D. S., xe2x80x9cStern Flap Powering Performance on the PC 1 Class Patrol Coastal, Full Scale Trials and Model Experiments,xe2x80x9d PATROL ""96 Conference Proceedings, New Orleans, La., (December 1996); Cusanelli, D. S.; xe2x80x9cIntegrated Wedge-Flap, an Energy Saving Device,xe2x80x9d 21st UJNR Marine Facilities Panel Meeting, Tokyo, Japan (May 1997); Cusanelli, D. S., and G. Karafiath, xe2x80x9cIntegrated Wedge-Flap for Enhanced Powering Performance,xe2x80x9d FAST ""97, Fourth International Conference on Fast Sea Transportation, Sydney, Australia, (July 1997); Cusanelli, D. S., xe2x80x9cStem Flap Installations on Three US Navy Ships,xe2x80x9d ASNE 1998 Symposiumxe2x80x9421st Century Combatant Technology, Biloxi, Miss. (January 1998); Cusanelli, D. S. and L. Hundley, xe2x80x9cStern Flap Powering Performance on a SPRUANCE Class Destroyer, Full Scale Trials and Model Experiments,xe2x80x9d Research to Reality in Ship Systems Engineering Symposium, Tysons Corner, Va. (September 1998); Cusanelli, D. S. and L. Hundley, xe2x80x9cStem Flap Powering Performance on a SPRUANCE Class Destroyer, Full Scale Trials and Model Experiments,xe2x80x9d Naval Engineers Journal, Vol. 111, No. 2 (March 1999), Cusanelli, D. S., S. D. Jessup and S. Gowing, xe2x80x9cExploring Hydrodynamic Enhancements to the USS Arleigh Burke (DDG 51),xe2x80x9d FAST""99, Fifth International Conference on Fast Sea Transportation, Seattle, Wash. (August 1999); Cusanelli, D. S., and G. Karafiath, xe2x80x9cEnergy Savings and Environmental Benefits of Stern Flaps on Navy Ships,xe2x80x9d ASNE Symposium: Marine Environmental Stewardship for the 21st Century, Arlington, Va. (October 1999); Cusanelli, D. S., and G. Karafiath, xe2x80x9cStem Flaps on Navy Ships, Fuel Savings and Environmental Benefits,xe2x80x9d IMT""99, Innovations in Marine Technology, New Orleans, La. (December 1999); Cusanelli, D. S., xe2x80x9cStern Flaps and Bow Bulbs for Existing Vesselsxe2x80x94Reducing Shipboard Fuel Consumption and Emissions,xe2x80x9d United Nations Environmental Programme (UNEP 2001), Brussels, Belgium (February 2001); Cusanelli, D. S., and G. Karafiath, xe2x80x9cStern Flapsxe2x80x9d, Professional Boat Builder Magazine, pages 81-87, (April/May 2001); Karafiath, G, D. S. Cusanelli, S. D. Jessup and C. D. Barry, xe2x80x9cHydrodynamic Efficiency Improvements to the USCG 110 Ft. WPB Island Class Patrol Boats,xe2x80x9d 2001 SNAME Annual Meeting Paper, Orlando, Fla. (October 2001).
The standard (traditional or conventional) stern flap is designed with parallel, linear (straight) leading and trailing edges for orientation of these linear edges perpendicular to the ship centerline. The present inventor was tasked to apply existing stern flap technology to U.S. Coast Guard ships such as the HAMILTON Class or FAMOUS Class, wherein the hull design includes a highly curved transom. The inventor found that the standard stern flap had its limitations and would be disadvantageous for the task at hand. A configuration involving a standard stem flap and a curved transom would present various practical problems and would not be propitious.
To elaborate, installation of a standard stern flap on a highly curved transom would necessitate recession of the leading edge of the standard stern flap, at its centerline, under the transom. Full-scale installation and implementation would be difficult, particularly with regard to the arrangement and attachment of the partially recessed appendage to the curved transom. Moreover, such application of a standard stern flap with respect to a curved transom would inherently fail to fully utilize the entire stern flap chord length. In principle, a stern flap itself produces drag, and the stem flap""s interactions with the hull, wave systems and propulsor produce the net decrease in required power. Generally, chord length is one of the parameters to be optimized; increase in effective ship length enhances reduction in ship wave resistance, and increase in stern flap total surface area increases the associated drag (resistance). The partial recess of the installed standard flap would directly limit the increased effective ship length associated with the stern flap installation. Furthermore, the partial recess of the flap would not make full use of the flap surface area.
In view of the foregoing, it is an object of the present invention to provide a stern flap which is superior to a standard stem flap for applications wherein a stem flap is being coupled with a marine vessel having a curved transom. The term xe2x80x9ccurved transom,xe2x80x9d as used herein, refers to a transom which is curved laterally, athwart, crosswise or transverselyxe2x80x94i.e., a transom at least a portion of which describes a curve, across the transom, wherein the curve lies in an imaginary geometric plane which cuts across the transom so as to be at an angle with respect to (that is, so as not to be coincident with) the imaginary geometric plane generally described by the transom itself. Typically, a xe2x80x9ccurved transomxe2x80x9d is a transom that xe2x80x9cbulgesxe2x80x9d so as to be approximately symmetrically curved in a bilateral direction.
The present invention features a stern flap which is contoured to fit a curved transom. The inventor, a naval architect employed by the U.S. Navy, conceived his invention based on his realization that the application of stern flap technology to the highly curved transom of the U.S. Coast Guard ships of interest (such as the HAMILTON Class or FAMOUS Class) would necessitate a new flap plan form design shape. The inventor initially investigated his contour stem flap concept by conducting model-scale tests on this hullform which is characterized by a highly curved transom. The inventor thus demonstrated that the performance of a traditional flap design, when applied to this kind of hullform, was inferior to that of his new contour shape.
According to typical embodiments of the present invention, an adjunctive device is for use in association with a nautical vehicle which includes a stern characterized by a stern curvature across the stern. The present invention""s adjunctive device includes an edge characterized by an edge curvature which at least substantially conforms with the stern curvature. The inventive adjunctive device is adaptable to association with the nautical vehicle so that the edge at least substantially adjoins the stern.
In accordance with many such inventive embodiments, the edge is a xe2x80x9cleading edge,xe2x80x9d and the edge curvature is a leading edge curvature. The inventive adjunctive device includes a xe2x80x9ctrailing edgexe2x80x9d which is characterized by a trailing edge curvature which at least substantially corresponds with the leading edge curvature. The nautical vehicle includes a bottom, the stern and bottom forming a crosswise junction which is characterized by the stern curvature. The inventive adjunctive device includes a lower surface which is at least substantially flat and is oppositely bounded by the leading edge and trailing edge. The distance generally across the lower surface between the leading edge and trailing edge is at least substantially constant. The inventive adjunctive device is adaptable to association with the nautical vehicle so that the nautical vehicle""s bottom and the adjunctive device""s lower surface are at least substantially flush, and so that the distance generally across the lower surface between the nautical vehicle""s crosswise junction and the adjunctive device""s trailing edge is at least substantially constant.
Many embodiments of the present invention provide a method of changing the hydrodynamic character of a hullform having a stern surface and a hull-bottom surface conjoinedly defining a curvilinear transverse stern edge. The inventive method comprises the steps of: (a) providing a flap having a curvilinear leading flap edge, a curvilinear trailing flap edge and a flap undersurface delimited by the leading flap edge and the trailing flap edge, wherein the curvilinearity of the leading flap edge is at least substantially equivalent to the curvilinearity of at least a portion of the transverse stern edge; and, (b) coupling the flap with the hullform so that the leading flap edge and the at least a portion of the transverse stem edge are at least substantially adjacent, thereby generally establishing a continuity between the hull-bottom surface and the flap undersurface.
The present invention affords several advantages when used in association with marine vessels having a stem characterized by a degree of lateral curvature, especially sterns characterized by larger degrees of lateral curvature. In accordance with typical embodiments the present invention, since both the leading and trailing edges of the flap match the transom radius of curvature, a constant chord length (as measured perpendicular to the transom knuckle) is maintained. Therefore, in inventive practice, full utilization is made of the flap chord length and total surface area.
Furthermore, conventional installation techniques (for effecting attachment of a stern flap to a marine vessel at the stern) are permitted by the present invention. The inventive geometric matching of the knuckle radius allows for surface installation of the contour stem flap on the transom, such installation involving only conventional welding of mostly flat plates that are at large angles to each other and to the hull; this is essentially the same technique presently utilized for installation of traditional flaps. In accordance with the present invention, the inventive contour stem flap can be separately manufactured and then installed (e.g., retrofitted) on an existing hull. Alternatively, a hull can be designed and manufactured xe2x80x9cfrom scratchxe2x80x9d in accordance with the present invention so as to include the inventive contour stem flap.
The inventor discloses certain aspects of his invention in the paper Dominic S. Cusanelli and Gabor Karafiath, xe2x80x9cAdvances in Stem Flap Design and Application,xe2x80x9d FAST 2001 (The Sixth International Conference on Fast Sea Transportation), Southhampton, United Kingdom, 4-6 Sep. 2001, incorporated herein by reference.
Other objects, advantages and features of this invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.